Reader devices are conventionally known which read codes such as characters from various objects to be read. The object to be read is, for example, a document with a plurality of sheets bound up. The document is, for example, a passport.
The conventional reader device is configured to illuminate a surface to be read of an object to be read with infrared light to pick up an image of a code on the surface to be read, thus acquiring an infrared light image. The infrared light image is subjected to reading processing such as OCR (Optical Character Recognize) to allow the code to be recognized. The use of infrared light as illumination light allows prints in black ink, which is likely to absorb infrared light, to be emphasized to make a background image relatively unclear. This makes the code in a sharper contrast with the remaining part of the image. Furthermore, a fraud can be detected by comparison with an image picked up by visible light and showing characters or graphics drawn with ink that absorbs infrared light and reflects visible light.
Furthermore, when an image of an object to be read is displayed on a monitor or the like, for example, to allow an operator to visually check the image, the object to be read is illuminated with visible light instead of infrared light to acquire a visible light image. Alternatively, like infrared light images, the visible light image may be subjected to OCR to allow the code to be recognized.
For example, Patent Literature 1 discloses a reader device configured to irradiate an object to be read with both infrared light and visible light. This conventional device uses visible light to generate a hologram image, while using infrared light to read a code printed in a layer under the hologram.
Furthermore, the reader device needs to avoid image pickup under a specular reflection condition. The specular reflection condition is such that the direction of image pickup coincides with the incident angle of illumination light, that is, the direction of specular reflection. When an image of a surface to be read is picked up under the specular reflection, reflected light is excessively intense and what is called “washed-out highlight” occurs. This may prevent the good image from being obtained. The “washed-out highlight” refers to white-out that occurs in a part of an image as a result of the saturated dynamic range of an imaging device. In this phenomenon, the visible light image whites out to prevent a subject from showing up in the image or to make the subject in the image difficult to see. In the conventional art, in order to avoid the specular reflection condition, the surface to be read is illuminated from the side and picked up from the front. This enables the reflection angle of illumination light (=incident angle) to be increased to avoid the specular reflection condition (see, for example, Patent Literature 2).
However, the conventional reader device poses the following problems in connection with deformation of the object to be read.
An object to be read such as a passport may wet with an owner's sweat, for example, when carried in the owner's pocket. The wetting and the subsequent drying or the like subjects the edge of the object to be read to wave-like deformation (corrugation). When such wave-like deformation occurs, imaging of the edge may be carried out under the specular reflection condition, resulting in washed-out highlight. If a code such as characters is present at the edge, the code may fail to appear clearly in the image. Thus, desirably, illumination is properly provided so as to suitably prevent the wave-like deformation of the edge to allow an image of the code at the edge to be picked up.
For example, passports are covered with a laminate or the like. Hence, washed-out highlight is likely to occur in an image of the passport under the specular reflection condition. Furthermore, in many of the passports, a code is printed so as to end in a corner of the corresponding page. The above-described wave-like deformation of the page is likely to be significant in the corner of the page. Thus, when an image of a passport subjected to wave-like deformation is picked up under illumination with visible light, a part of the code located in the corner may be difficult to see as a result of washed-out highlight. In particular, one or two characters in the corner are difficult to see. Thus, desirably, illumination is properly provided so as to prevent possible washed-out highlight in the part of the code located at the edge.
To avoid the above-described problem, the device may include a cover for holding the object to be read. However, when the object to be read is a passport or the like, a reading operation needs to be performed quickly. Thus, desirably, illumination can be properly provided without the use of a cover or the like, even if the object to be read slightly floats.
Furthermore, for miniaturization of the device, an optical path through which images are read may be bent using a mirror, to reduce the volume of the whole device. In this case, the mirror is arranged between the surface to be read and a camera. Reflected light from the surface to be read is bent by the mirror before reaching the camera. However, when the mirror is provided, illumination light is also reflected by the mirror and impinges on the surface to be read of the object to be read. As a result, illumination unevenness may occur to degrade the reading ability or make a display image difficult to see.